The present invention relates to a high breakdown voltage semiconductor device having a dielectric isolation structure, particularly, a high breakdown voltage semiconductor device dielectric isolation type substrate.
FIG. 1 is a cross sectional view showing a conventional lateral diode using a dielectric isolation type substrate. As shown in the drawing, a dielectric isolation type substrate is prepared by stacking a semiconductor substrate 1 and an n-type semiconductor substrate 2 of a high resistivity one upon the other with an insulating film 3 interposed therebetween. A p-type anode region 4 and an n-type cathode region 5 are formed in a surface region of the n-type semiconductor substrate 2 of the dielectric isolation type substrate. Also, an n.sup.+ -type impurity region 6 and a p.sup.+ -type impurity region 7 are formed selectively on each of the anode region 4 and the cathode region 5. Further, an anode electrode 8 is formed in ohmic contact with the surface of each of the n.sup.+ -type impurity region 6 and the p.sup.+ -type impurity region 7 within the anode region 4. Likewise, a cathode electrode 9 is formed in ohmic contact with the surface of each of the n.sup.+ -type impurity region 6 and the p.sup.+ -type impurity region 7 within the cathode region 5.
Where the semiconductor substrate 2 has a thickness of 15 .mu.m in the lateral type diode of the construction shown in FIG. 1, a reverse recovery time t.sub.rr is not longer than 0.18 .mu.sec (t.sub.rr .ltoreq.0.18 .mu.sec), supporting that the reverse recovery can be achieved at a high speed. However, a maximum reverse recovery current I.sub.MAX is not larger than 0.5A (I.sub.MAX .ltoreq.0.5A), supporting that the maximum reverse recovery current I.sub.MAX is low so as to allow the lateral diode to be destroyed easily.
As described above, the lateral diode using a conventional dielectric isolation type substrate is defective in that a parasitic thyristor is formed by the presence of the n.sup.+ -type impurity region 6. The parasitic thyristor thus formed is latched up so as to lower the maximum reverse recovery current I.sub.MAX so as to allow the lateral diode to be destroyed easily.